The installed cost of conventional offshore permanent platforms has become a major deterrent to their use, running as high as a billion dollars as in the case of the C.O.G.N.A.C. platform installed directly in the Gulf of Mexico. In installing such a platform, the jacket is floated to the installation site on launch barges after which the jacket is launched to a floating condition. It is then positioned by a crane barge, flooded and sunk in place. Piling anchors are then driven with a crane barge, the jacket levelled and welded to the piling which are then grouted. The machinery deck is floated to the site on a deck barge and lifted into place on the installed jacket by a crane barge. Such a platform installation is considered to be permanent in the sense that, as a practical matter, it is not moved to another site after its usefulness at the installed site ceases. While machinery decks can and are moved from jacket to jacket and drilling decks are replaced by production decks, the piling used to anchor a jacket is practically impossible to remove due to grouting and hence jackets are salvaged on an extremely rare basis. However, since jackets must be removed when their use ceases, the common practice is to cut loose, tow to deep water and then to sink them.
On the other hand, mobile platforms which have their own flotation and propulsion systems are very suitable for purposes that require frequent movement from one site to another because their erection and transport costs are relatively small. However the daily cost of mobile platforms virtually exclude them from all applications except high risk, high return applications, such as oil and gas well drilling.
Therefore, there is need for a safe, easily transportable and affordable semi-permanent offshore platform. Such need includes temporary facilities during: the exploration for and early production of oil and gas; the early life of an oilfield; early warning systems for defense purposes; navigation installations; communication installations; marine research installations and previously uneconomical industrial and commercial application.
Therefore, a principal feature of this invention is to provide a system for the efficient transport and reversible erection of a safe but lightweight offshore platform structure.
Another feature of this invention is to provide means for the transport of the platform structure.
Another feature of this invention is to provide means for the safe and efficient erection of the platform structure.
Another feature of this invention is to provide anchoring and guying means that do not interfere with normal operation of the platform facilities.
Another feature of this invention is to provide emergency guying means that can be effected safely and quickly before and during storm conditions.
Another feature of this invention is to provide means to safely and easily position and lower the base member and the structural column to the ocean floor.
Another feature of this invention is to provide means to assemble additional sections of the column as may be required by deeper water locations or to lower the center of gravity during transport.
Another feature of this invention is to provide means to adjust the platform to a preferred height above the water surface.
Another feature of this invention is to provide a means to adjust the column to a vertical position if the base member is positioned on a non-level ocean floor.
Another feature is to provide a method for deploying and retrieving an anchoring system without necessarily using conventional service boats.